High-pressure discharge lamp including halides of tantalum and dysprosium

ABSTRACT

A high-pressure metal-halide discharge lamp (1) having a mean arc power  been 60 and 140 W/mm arc length includes a discharge vessel (2), two electrodes (5,6), a fill of mercury, at least one noble gas, at least one halogen, cesium, and tantalum and dysprosium for forming metal halides to produce light with a color temperature between 400 and 700 K at a wall load of between 40 and 85 W/cm 2  wall area. The tantalum maintains the halogen cycle process at relatively low wall loads, and thus prevents blackening and devitrification of the bulb, while dysprosium provides a high radiation flux in the visible range of the optical spectrum and thus optimizes color reproduction. At a wall load of between 40 and 85 W/cm 2 , optimum results are attained if the fill contains from 0.2 to 1.5 mg of tantalum and dysprosium per cm 3  of vessel volume, in a weight ratio of tantalum to dysprosium of between 0.3 and 1.5. As a result, lamp service life of 1500 hours at a color temperature of 5500 K are attained.

The invention relates to a high-pressure metal-halide discharge lampwith a mean arc power between 60 and 140 W/mm arc length, for fitting inoptical systems, as generically defined by the preamble to claim 1.High-pressure metal-halide discharge lamps of this type are usedparticularly in projection systems (slide projectors, overheadprojectors, amateur and professional movie projectors) and glass fiberlighting systems (endoscopy, microscopy, effect lighting for film andtelevision), where light with color temperatures between 4000 and 7000 Kand good to very good color reproduction in all color temperature rangesare needed. They are distinguished by a very short arc light (a fewmillimeters) and maximum light densities (on average, several tens ofkcd/cm²), which predestines them for installation in reflectors or otheroptical imaging systems.

European Patent Disclosure EP 0 193 086 and German Patent DisclosureDE-A 4 040 858 disclose high-pressure metal-halide discharge lamps withshort arcs and correspondingly high light densities, which produce lightwith a spectral composition similar to daylight. However, theirdisadvantage is that these lamps have average service lives of only afew hundred hours.

The object of the invention is to create a high-pressure metal-halidedischarge lamp that has an average service life of at least 1000 hoursof operation, has a very short arc with very high light density, and hasa color temperature between 4000 and 7000 K = with very good colorreproduction--and that attains this goal with the fewest possibleelements in its filling.

This object is attained by the characteristics of the body of claim 1.Other advantageous characteristics are recited in the dependent claims.

The high-pressure metal-halide discharge lamp according to the inventionis operated at specific arc powers between 60 and 140 W/mm of arc lengthand at comparably low wall loads of between 40 and 85 W per cm² of wallarea. With conventional fillings, at wall loads below or aboveapproximately 60 W/cm², bulb blackening or devitrification occurs withina short time, and the value for these limits can vary depending on thecooling. As a result, the useful light flux drops, and the lamp life isshortened.

To the filling of the lamp according to the invention--which comprisesmercury, at least one noble gas and at least one halogen andcesium--tantalum and dysprosium are added, preferably in a ratio byweight of between 0.3 and 1.5; the total quantity of these two importantadditives to the filling is advantageously between 0.2 and 1.5 mg/cm³.Tantalum maintains the halogen cycle process even at relatively low wallloads and thus largely prevents blackening and devitrification of thebulb, so that a long average service life can be attained. Tantalum alsocontributes to the continuum proportion in the optical spectrum.Dysprosium, with its multi-line spectrum, assures a high radiation fluxin the visible range of the optical spectrum. By means of the additionof tantalum and dysprosium according to the invention, the tendency todevitrification and blackening of the bulb is accordinglyminimized--that is, the mean service life is correspondinglyprolonged--and the light flux and the color reproduction are optimized.

If the color temperature is to be lowered and/or particularly good colorreproduction is to be attained, then optionally lithium can be added inaddition, in a proportion up to 0.2 mg/cm³ of the vessel volume; thisincreases the red proportion in the radiation, which can be advantageousparticularly when the lamp is used in a dichroitic cold-light reflector,which raises the color temperature of the reflected radiation somewhatcompared with the total radiation of the discharge. Moreover, lithium isan atomic line radiator, which radiates preferably in the hot arc coreand is therefore projected especially efficiently by suitably focusingspecial reflectors that project only the inner arc core.

For arc stabilization, the discharge vessel can contain cesium in aproportion up to 0.8 mg/cm³ of the vessel volume. Iodine and bromine ina molar ratio between 0.2 and 2 are preferably used as the halogens.

The invention will be described in further detail in terms of theexemplary embodiments below.

The drawing shows a sectional side view through a high-pressuremetal-halide discharge lamp according to the invention.

In the drawing, a high-pressure metal-halide discharge lamp 1 accordingto the invention with a power consumption of 400 W, of a kind that canbe used in a reflector system, is shown schematically (not to scale).The discharge vessel 2 of quartz glass is essentially spherical in formand at each of two diametrically opposed points has a neck 3, 4, intowhich pronglike tungsten electrodes 5, 6 are sealed in by means ofsealing foils 7, 8 of molybdenum. The ends of the sealing foils 7, 8remote from the discharge chamber are welded to current supply leads 9,10, which on installation in a reflector system are connected with theelectrical terminals in the reflector.

Table 1 shows two fillings according to the invention of the dischargevessel 2 of a 400 W lamp, with the service lives attained thereby, alongwith the lighting specification data of this lamp. By adding lithium tothe filling 2, the color temperature is lowered by approximately 500 Kcompared with the filling 1.

                  TABLE 1                                                         ______________________________________                                                          Filling 1                                                                            Filling 2                                            ______________________________________                                        Li in mg            --       0.005                                            I.sub.2 in mg       0.9      0.92                                             Br.sub.2 in mg      0.75     0.75                                             Cs in mg            0.22     0.22                                             Dy in mg            0.24     0.24                                             Ta in mg            0.16     0.16                                             Hg in mg            30.5     30.5                                             Ar in mbar          450      450                                              Discharge vessel volume in ml:                                                                    1.3      1.3                                              Power consumption in W:                                                                           400      400                                              Wall load in W/cm.sup.2                                                                           68       68                                               Specific power in W/mm                                                                            95       95                                               arc length:                                                                   Color temperature in K:                                                                           5500     5000                                             Service life in h:  1500     1500                                             Electrode spacing in mm:                                                                          4        4                                                Light yield in lm/W:                                                                              70       69                                               Mean light density in kcd/cm.sup.2 :                                                              30       30                                               Arc drop voltage in V:                                                                            55       55                                               Color reproduction index Ra:                                                                      90       90                                               ______________________________________                                    

Another exemplary embodiment relates to a high-pressure metal-halidedischarge lamp according to the invention with a power consumption of270 W. It differs in its design from the lamp shown in the drawingessentially only in having a smaller discharge volume and a shorterelectrode spacing and has therefore not been shown in the drawing.

Table 2 shows a filling according to the invention of the dischargevessel of a 270 W lamp, with the light specification data of this lamp.

                  TABLE 2                                                         ______________________________________                                        Li                    0.005  mg                                               I.sub.2               0.75   mg                                               Br.sub.2              0.36   mg                                               Cs                    0.1    mg                                               Dy                    0.13   mg                                               Ta                    0.08   mg                                               Hg                    13.2   mg                                               Ar                    450    bar                                              Discharge vessel volume:                                                                            0.55   ml                                               Power consumption:    270    W                                                Wall load:            81     W/cm.sup.2                                       Specific power        117    W/mm                                             Color temperature:    5000   K.                                               Service life:         1000   h                                                Electrode spacing:    2.3    mm                                               Light yield:          70     lm/W                                             Mean light density:   35     kcd/cm.sup.2                                     Arc drop voltage:     45     V                                                Color reproduction index Ra:                                                                        80                                                      ______________________________________                                    

I claim:
 1. A high-pressure metal-halide discharge lamp (1), having amean arc power between 60 and 140 W/mm arc length for fitting in opticalsystems, having a discharge vessel (2) of high-temperature-prooftransparent material, two high-temperature-proof electrodes (5, 6), anda filling that comprises mercury, at least one noble gas, at least onehalogen, cesium, and further metals for forming metal halides,characterized in that to produce light with a color temperature between4000 and 7000 K, at a wall load at the lamp (1) between 40 and 85 W/cm²at wall area, the filling contains tantalum and dysprosium as furthermetals.
 2. The high-pressure metal-halide discharge lamp of claim 1,characterized in that the discharge vessel contains tantalum anddysprosium in a ratio by weight of between 0.3 and 1.5.
 3. Thehigh-pressure metal-halide discharge lamp of claim 1, characterized inthat the discharge vessel contains tantalum and dysprosium, and the sumof the filling quantities of the two components is between 0.2 and 1.5mg/cm³ of the vessel volume.
 4. The high-pressure metal-halide dischargelamp of claim 1, characterized in that the discharge vessel additionallycontains lithium.
 5. The high-pressure metal-halide discharge lamp ofclaim 4, characterized in that the filling quantity of the lithiumamounts to up to 0.2 mg/cm³ of the vessel volume.
 6. The high-pressuremetal-halide discharge lamp of claim 1, characterized in that thedischarge vessel, as halogens for the halide compounds, contains iodineand bromine in a molar ratio between 0.2 and
 2. 7. The high-pressuremetal-halide discharge lamp of claim 1, characterized in that thedischarge vessel contains cesium in a quantity up to 0.8 mg/cm³ of thevessel volume.